1. Field Of The Invention
The present invention relates to a method of providing a low-stress region adjacent to an embedded read sensor to reduce stress on the read sensor during a lapping process.
2. Description Of The Related Art
The heart of a computer is a magnetic disk drive that includes a magnetic disk, a slider where a magnetic head assembly including write and read heads is mounted, a suspension arm, and an actuator arm. When the magnetic disk is stationary, the slider is biased by the suspension arm into contact with the surface of the magnetic disk. When the magnetic disk rotates, the rotating magnetic disk swirls air at an air bearing surface (ABS) of the slider, causing the slider to fly on an air bearing. When the slider flies on the air bearing, the actuator arm swings the suspension arm to place the magnetic head assembly over selected circular tracks on the rotating magnetic disk, where signal fields are written and read by the write and read heads, respectively. The write and read heads are connected to processing circuitry that operates according to a computer program to implement write and read functions.
An exemplary high performance read head employs a read sensor for sensing the signal fields from the rotating magnetic disk. The most recently explored read sensor, a giant magnetoresistance (GMR) sensor, comprises a nonmagnetic Ni—Cr—Fe seed layer, ferromagnetic Ni—Fe/Co—Fe sense layers, a nonmagnetic Cu—O spacer layer, a ferromagnetic Co—Fe reference layer, a nonmagnetic Ru antiparallel (AP) exchange-coupling layer, a ferromagnetic Co—Fe keeper layer, and nonmagnetic Cu and Ta cap layers. Crystalline reconstruction occurring in the Ni—Cr—Fe seed and Ni—Fe sense layers causes the two layers to behave as if a monolayer film exhibiting coarse polycrystalline grains with a strong <111> texture, thus leading the GMR sensor to exhibit low sensor resistance and a high GMR coefficient. Intrinsic and extrinsic uniaxial anisotropies of the Co—Fe reference and Co—Fe keeper layers, and their ferromagnetic/ferromagnetic AP exchange coupling occurring across the Ru AP exchange-coupling layer cause the Co—Fe reference and Co—Fe keeper layers to be self-pinned, thus leading the GMR sensor to operate properly. Alternatively, an antiferromagnetic Pt—Mn pinning layer is sandwiched into the Co—Fe keeper and Cu cap layers. Ferromagnetic/antiferromagnetic exchange coupling occurring between the Co—Fe keeper and Pt—Mn pinning layers causes rigid pinning to the Co—Fe keeper layer, thus reinforcing the AP exchange coupling pinning and ensuring the proper sensor operation.
In the prior art, the fabrication process of the magnetic head assembly typically includes building the read head on a wafer, building-the write head on the wafer, slicing the wafer into rows, mechanically lapping and overcoating the rows, and slicing the rows into sliders. During building of the read sensor on the wafer, the GMR sensor is conventionally formed using three photolithographic patterning processes.
To illustrate, FIG. 1 shows a top view of an in-process GMR sensor structure 100 according to the prior art. FIGS. 2 and 3 are cross-sectional views of the in-process GMR sensor structure 100 formed in the prior art on planes perpendicular and parallel, respectively, to its ABS. In the first process, a region 101 is formed with a height of about 3,000 nm to 5,000 nm, much larger than the designed height of the GMR sensor 100 (100 nm). An insulating film (Al2O3) is deposited outside the region 101. In the second process, two regions 102 are formed with a separation equivalent to the designed width of the GMR sensor 100 (120 nm). Longitudinal bias and first conducting layers are deposited into the two regions 102. In the third process, two regions 103 are formed on top of the two regions 102. Second conducting layers are deposited into the two regions 103.
FIGS. 4 and illustrate cross-sectional views of the completed GMR sensor and magnetic head, respectively, in the prior art on a plane perpendicular to its ABS, after mechanical lapping and overcoating. During the mechanical lapping, the height of the GMR sensor 100 is reduced from about 3,000 nm to a designed height of as small as 100 nm. The mechanical lapping is monitored by measuring the resistance of an electrical lapping guide (not shown), having the same structure and geometry as the GMR sensor 100 but located more than 100 μm away from the GMR sensor 100, which is terminated as its resistance substantially increases from about 16 to about 40Ω-50Ω. Hence, in the prior art, the designed width of the GMR sensor is defined by photolithographic patterning while its designed height is defined by the mechanical lapping.
There are several disadvantages in forming the GMR sensor according to the prior art. First, electrostatic discharge (ESD) damage may occur during the mechanical lapping indicated by an unwanted substantial increase in the resistance of the GMR sensor. The GMR sensor 100 may thus be not viable at all. Second, the magnetic moments of sense, reference, and keeper layers at the ABS may substantially decrease by uncertain amounts, white the pinning layer may corrode, due to the exposure of the ABS to the chemical solution and air. The designed magnetic moments and desired exchange-coupling may not be attained at the ABS, thus substantially reducing the signal sensitivity of the GMR sensor. Third, all the various layers of the GMR sensor 100 may be recessed differently and an unwanted stepped ABS is formed, due to their different mechanical lapping rates. A protection overcoat 200 of the GMR sensor 100 may thus not adhere well on this stepped ABS, thus causing concerns on the contact of the GMR sensor with the rotating magnetic disk during sensor operation. Because of these problems, the GMR sensors 100 formed in the prior art may not be suitable for magnetic recording at ultrahigh densities.
Finally, the mechanical stresses during the mechanical lapping may also produce electrical overstress (EOS) which may cause the pinning field of the sensor to deviate from being perpendicular to ABS or even to be oriented in a “flipped” or reversed orientation. The latter is referred to as “amplitude flip”. Referring ahead to FIG. 15, the problem is depicted more clearly in a graph 1 500. Graph 1500 shows a resistance curve 1502 and an amplitude curve 1504 which are based on signals monitored during the lapping process. As revealed, the amplitude of the read sensor “flips” back and forth between positive and negative polarities at or around the time when the read sensor is exposed from the lapping.
Accordingly, what is needed is a method that reduces the risk of ESD damage and the possibility of amplitude flip in the GMR sensor. What is further needed is a method that controls the sensor resistance, minimizes the losses in the magnetic moments, eliminates corrosion, and precisely controls the height of the GMR sensor.